The invention relates to a rotary damper, more particularly, to a rotary damper for producing rotational resistance on a hinge shaft of an opening-closing member.
A rotary damper is often used for applying the rotational resistance to a hinge shaft of an opening-closing member, such as a console box and grove box in a car, a display panel of a lap-top computer and a service lid of a printer, so that the opening-closing member is not suddenly closed or opened.
As this kind of a rotary damper, a rotary damper using a viscous liquid is known. For example, Japanese Patent Publication (Tokkai) No. 64-30938 discloses a rotary damper including a cylindrical member provided with a wall along a radial line on an inner peripheral surface of a cylindrical chamber, and a rotor member provided with vanes moving along the inner peripheral surface of the cylindrical chamber, so that the vanes receive the resistance of a viscous fluid filled in the cylindrical chamber when the rotor member rotates relative to the cylindrical member.
In this type of the rotary damper, when a large damping torque is required to be generated within a limited space, the liquid must have a high viscosity. Thus, the rotary member including the vanes is required to have high torsional strength. In order to obtain the rigidity for this end, although a metal is a useful material for the rotor member, such a small part made of the metal results in a high manufacturing cost.
In view of the above disadvantages, the present invention has been made and an object of the invention is to provide a rotary damper, wherein the torsional strength of a rotor member is greatly improved without increasing a manufacturing cost.
Further objects and advantages of the invention will be apparent from the following description of the invention.